1. Field of the Invention
This invention relates generally to a method of and an apparatus for drying a continuous-length beltlike article, such as an elongated strip of cloth, an elongated strip of paper, a slide fastener tape, a surface-type fastener tape, or the like, and an induction heater equipped with rotary drums. More particularly the invention relates to an effective technology to dry such a beltlike article after washed or dyed.
2. Description of the Related Art
Attempts have hitherto been made to dry an elongated beltlike cloth or paper article containing moisture, particularly by heating the beltlike article to evaporate water. To this end it is currently known that hot or heated air is blown out over the beltlike article and that the beltlike article is wound around rotary drums that are heated, for example, by introducing steam into the rotary drums, by placing an electric heater in each rotary drum, or by heating each rotary drum from its outside by electromagnetic induction. These known technologies will now be described specifically with reference to FIGS. 8, 9 and 10.
FIG. 8 shows a prior art apparatus for drying a continuous-length beltlike article (slide fastener tape) 32 with hot air. In this drying apparatus, the beltlike article 32 is continuously fed as wound in a zigzag pattern around several pairs (only one pair are illustrated) obliquely spaced rollers 31, 31 arranged horizontally one pair behind another. Downstream of the roller assembly, a nichrome-wire heater 33 and a fan 34 are located to blow out hot air over the beltlike article 32 in the direction indicated by arrows.
FIG. 9 shows another prior art drying apparatus in which the beltlike article 32 is dried by the heat of a pair of vertically spaced rotary drums 35, 35 heated with steam. During the drying, the beltlike article 32 is wound several times around the two rotary drums 35, 35, and the rotary drums 35, 35 are heated from inside with steam supplied from a steam boiler 36 via a supply pipe 37 and discharged from a discharge pipe 38. Designated by 39 is an adiabatic material covering the supply pipe 37.
FIG. 10 is a side view, with its upper half in cross section, of still another prior art drying apparatus in which a non-illustrated beltlike article is dried by the heat of rotary drums (only one shown) 41 heated from outside by electromagnetic induction heating. FIG. 11 is a fragmentary front view of FIG. 10. During the drying, the non-illustrated beltlike article is wound around the rotary drums 41, whose each shaft is rotatably supported at only one end by a bearing 40. A pair of heating coils 42, 42 are located adjacent to the outer circumferential surface of each rotary drum 41 for induction heating.
However, these prior art technologies have the following disadvantages.
The first-named apparatus is large in entire structure and hence requires an extensive area (e.g., about 15 m in the longitudinal direction) for installation, thus causing a poor thermal efficiency (less than 10%), an increased cost of running, and nonuniform temperature of hot air (varies by plus and minus 20%). For these reasons, the once dyed beltlike article would be discolored on a certain occasion. At the time to start the apparatus, the temperature of hot air would rise very slowly at the time to start the apparatus, requiring a long time to initiate drying operation. At the time to stop the apparatus, it would be lowered very slowly, causing the dyed beltlike article to be overheated and discolored due to thermal inertia.
In the second-named apparatus, the appurtenant work for installation of the steam boiler 36, the adiabatic pipe 37, ect. would be on a large scale, and the individual rotary drum 35 must be in the form of a pressure-resistant vessel, which is burdensome. The joint between the individual pipe 37, 38 and the individual rotary drum 35 is a connecting structure between a fixed part and a rotating part, which structure would be a cause for pressure leakage. Also the cost of facility installation would rise, and the thermal efficiency would be bad, thus remarkedly increasing the running cost. Further, since the facility cannot be moved easily, it is difficult to change the layout of the factory. Even when the heating temperature is to be varied commensurate with the rate of drying process, it is very difficult to control the temperature by the amount of steam supply, and there is a large danger in operation as high-temperature steam is used.
Furthermore, the method for performing induction heating the individual rotary drum from outside is a virtually effective solution to the problems in case of hot air or steam. However, in the induction heating method, since heating is performed locally, both the temperature rise to start the drying operation and the cooling down to stop the drying operation are very slow, and the thermal efficiency also is poor. If the individual rotary drum is heated while it is stopped, only a part of the circumferential surface of the rotary drum is heated, thus causing an irregular thermal distribution and hence distorting the rotary drum 41. Additionally, since the heating coils 42 are located adjacent to the outer circumferential surface of the rotary drum 41, it is difficult to wound the beltlike article around the rotary drum 41.